Aerodynamics

Archean simulates realistic, flight-sim-grade aerodynamic forces on any vehicle moving through a fluid — air or water. The engine produces lift, drag, stability, control authority, buoyancy, and even re-entry heating, all from the actual shape of your build. There are no special "wing blocks" or hidden stats: if it looks like a wing and is placed like a wing, it flies like a wing.

How It Works

The shape field (cross-section model)

When you finish editing a build, the engine takes a snapshot of its outer shape by scanning it from the six axis directions (like a cubemap) and turning the result into a set of small surface patches. Each patch knows its position, the direction it faces, its area, and — crucially — how deep the body is behind it (its cross-section).

This snapshot is cached and only rebuilt when the build changes (you add/remove blocks, a control surface moves, or the build takes damage). Per-frame flight physics just reads the cached patches, so the cost stays bounded no matter how complex your vehicle is — a 300-meter airliner with hundreds of colliders is just as cheap to fly as a small fighter. The scan resolution scales automatically with the vehicle's size.

Three promises follow — and the engine keeps them exactly, not approximately:

• How you build a shape never changes how it flies — only the final shape does. A 10 × 10 × 1 wing made from one big block or from a hundred small ones gives a bit-for-bit identical result: the same forces and the same moments, to the last digit. Subdivision, block count, and how geometry is split or merged are completely invisible to the airflow — only the outer silhouette and cross-section matter.
• Air and water are the same physics — there is no separate "water path." The model samples the fluid density at each surface and feeds it into the same lift-and-drag equations. Air, the waterline, and deep water are just points on one continuous density scale, so a wing smoothly becomes a hydrofoil as it submerges — nothing switches over.
• Material is invisible to flight. Steel, aluminium, composite — a flat plate is a flat plate. Material affects only mass and buoyancy, never lift or drag — it changes how the plane is balanced, not how it flies.

Only the outer shell is scanned. Interior blocks are never exposed to the airflow, so they add zero aerodynamic drag or cost — and because the model reads the solid thickness behind a surface (a sealed cavity counts as solid body), a hollow shape flies exactly like its solid version. Fill, or hollow out, your interiors freely; it never changes how the craft flies.

Lift

A surface generates lift (acts like a wing) when its cross-section is thin — the solid front-to-back depth at that surface is small compared to the vehicle's size. A wing is thin top-to-bottom but broad in span and chord, so it lifts. A fuselage is deep in every direction, so it only drags.

• Lift follows a realistic lift curve: it rises with angle of attack, then stalls past roughly 15°, after which lift drops and drag climbs sharply — just like a real airfoil.
• Lift is two-sided: a wing exposed to the air on both faces produces full lift; a wing whose underside is buried against the fuselage still lifts, at reduced strength.
• Separate surfaces each lift on their own. A twin tail, stacked (biplane) wings, or a fin lined up behind another along the same axis are read as the distinct thin surfaces they are — the air gap between them is not counted as solid body, so every one of them works.
• Lift is computed at each surface's location, so it naturally produces the right pitch, roll, and yaw moments about your center of mass.

To make a wing, make it geometrically thin. A broad, flat planform only a block or two thick will lift. A chunky, deep wing will mostly drag. How it is subdivided or what it is made of does not matter — only the cross-section.

Drag

Drag comes from several physical sources, combined automatically:

The key new behavior is fineness-based streamlining. The engine measures how slender each surface is — how far the body extends along the flow versus how thin it is across it:

• A slender shape (a pointed nose, a wing's sharp leading edge, a long thin fuselage moving forward) keeps the airflow attached and has very low form drag.
• A bluff shape (a cube, a flat plate held broadside like an airbrake, a blunt nose) has full form drag.

This is purely geometric — it reads your build's actual cross-section, so streamlining your nose and edges genuinely pays off.

Use slopes, corners, and bevels to taper noses and leading/trailing edges. A streamlined shape can have a tenth of the form drag of a blunt one at the same frontal size.

Compressibility (high speed)

The model is regime-aware. As you approach and exceed the speed of sound (which depends on air temperature), pressure on forward-facing surfaces rises through the transonic and supersonic range, and wing lift fades supersonically (you rely more on body lift and control deflection). This makes high-Mach flight feel distinctly heavier and less responsive, as it should.

Stability — emergent, not scripted

There is no artificial "keep it pointing forward" damping. Stability is a real, emergent result of where your surfaces are:

• A horizontal stabilizer mounted behind the center of mass meets the airflow at an angle whenever the nose pitches up or down, generating a restoring force that pushes the nose back. This is automatic pitch stability.
• A vertical stabilizer (tail fin) does the same for yaw whenever the vehicle sideslips.
• Rotational damping (resistance to tumbling) also emerges naturally — surfaces far from the center of mass move fast through the air when the vehicle spins, and the resulting forces oppose the spin.

Because it is real physics, static stability depends on your center of mass. An aircraft is stable when its center of mass sits at or slightly ahead of the wing's lift center, and unstable when the mass is too far aft — exactly like a real plane (and a real RC model). See Flying Well below.

The old artificial high-speed angular stabilization is gone for builds using this model. If your plane feels twitchy or won't settle, it is a balance problem, not the engine fighting you — move mass forward or add tail area.

Control surfaces & authority

Control surfaces (Ailerons used as ailerons, elevators, or rudders) are mounted on hinges and deflect in real time. The engine re-evaluates a deflected surface's aerodynamics at its current angle every frame, so:

• A deflected elevator immediately changes the airflow over the tail and pitches the aircraft.
• Authority scales with the surface's area, its distance from the center of mass (lever arm), and air density × speed².

For strong control: make control surfaces large and mount them far from the center of mass. An elevator at the very tail has far more pitch authority than one near the wing. Faster, denser air gives more authority — controls go soft at low speed and high altitude.

Damage-aware aerodynamics

Battle damage changes how a surface flies. As a panel is deformed or holed (and increasingly as it is destroyed):

• It sheds lift — a wrecked wing stops flying.
• It loses streamlining and pressure recovery, and drags more (it sheds a turbulent wake).

Because lift and drag are computed per-surface, asymmetric damage has the right effect: a wing shot up on one side both rolls the aircraft (lift loss on that side) and yaws it (extra drag on that side). Symmetric, redundant designs survive combat better.

Buoyancy

Buoyancy is the upward force on submerged blocks, computed per collider from the volume of fluid each block displaces.

F_buoyancy = V_displaced × ρ_fluid × g

• Each block's displaced volume = its volume × its material's volume displacement ratio (see Materials).
• Damaged blocks lose almost all of their buoyancy.
• Buoyancy is applied where the blocks actually are, so uneven submersion tilts the vessel — a self-righting effect for well-shaped hulls.

Water

Water is not a special case. The model samples the fluid density at every surface — air above the waterline, water below, blended smoothly across it — so the same lift-and-drag model simply produces much larger forces underwater, where the fluid is ~800× denser than air. Nothing is hard-coded for "being in water":

• A wing becomes a hydrofoil: it lifts and drags underwater exactly as it does in air, only far more strongly. Control surfaces keep working underwater, so a submarine steers with the same fins and ailerons a plane uses.
• Drag is enormous and grows with the square of speed, so a body entering water decelerates hard and a buoyant hull is naturally held back instead of rocketing out — no artificial damping required.
• Rotational damping comes straight from the same model: surfaces far from the center of mass move fast through the dense fluid when the craft turns or tumbles, so boats and submarines settle naturally.

Because the forces scale with density, hitting water at speed is a real impact. A fast belly-flop loads the whole contacting face far past what the structure can take and crumples or destroys it, exactly like hitting solid ground — so enter the water at a shallow angle and slow down first.

Re-entry heating

Moving fast through air heats forward-facing surfaces toward the stagnation (recovery) temperature, which rises with the square of speed. It is gentle at supersonic speeds but explosive at re-entry speeds, and each material burns up past its own thermal limit — so a heat shield, a steep-but-survivable re-entry angle, and bleeding off speed high up all matter.

Blocks and Materials

Materials

Material choice affects mass and buoyancy — and therefore balance — but not lift or drag:

• Lead is dense and fully displacing — ideal as nose ballast to move your center of mass forward (or as keel weight in a boat), but it sinks.
• Composite is light with moderate displacement — the best general floater.
• Steel/Aluminium/Titanium barely displace fluid — strong and light, but contribute almost no buoyancy.

Because material does not change aerodynamics, you choose materials for strength, weight, heat resistance, and balance — not for flight performance.

Block shapes

Slopes, corners, and pyramids occupy half a cube and are lighter. Aerodynamically they matter because they let you taper surfaces — turning a blunt, draggy face into a slender, streamlined one. Use them on noses and wing edges.

Frame beams

Frame beams (the structural bars at frame edges) are aerodynamically invisible — no lift, no drag, no buoyancy. Use them freely for internal structure.

Aerodynamic Components

Aileron

The Aileron is a hinged control surface used as an aileron, elevator, or rudder. Input is a value from -1.0 to +1.0 (rotation −45° to +45°) via its data port.

• It computes its own control force and is excluded from the main shape field, so it never double-counts and always delivers full authority even when surrounded by structure.
• You can build the fixed part of a wing or tail from blocks (which the field handles) and put ailerons at the trailing edge for control.

Propeller

The Propeller generates thrust in air or water and is excluded from the shape field (it has its own model). Key behaviors: thrust scales with fluid density and disc area; ground effect boosts thrust up to +50% near terrain; spinning blades create gyroscopic resistance to reorientation; thrust is capped at 100,000 N.

Thruster & RCS

Chemical Thrusters are unaffected by aerodynamics and work the same in atmosphere and vacuum. RCS thrusters lose nearly all effectiveness in dense fluids (attenuation ≈ e^−ρ×4) — they are for space.

Flying Well

Building wings

• Make the wing geometrically thin — a broad, flat planform a block or two thick. Thinner cross-section = cleaner lift.
• Give it span and chord; a long, broad wing lifts more and stalls more gently.
• Material and block count don't matter for lift — build for strength and weight.
• Taper the leading and trailing edges with slopes to cut drag.

Balancing for stable flight

This is the single most important thing for a plane that flies well:

• Keep the center of mass at or slightly ahead of the wings. Add dense mass (e.g. lead or heavy components) toward the nose to pull it forward — real aircraft carry their engine up front for exactly this reason.
• A tail-heavy aircraft (mass too far aft) is unstable: it pitches and yaws divergently and is exhausting to fly.
• Mount horizontal stabilizers well behind the center of mass for pitch stability, and a vertical fin for yaw stability. More tail area and a longer tail boom = more stability.
• If a build won't settle down, move mass forward or add tail area before blaming the controls.

Control authority

• Bigger control surfaces, mounted farther from the center of mass, give more authority.
• Put elevators at the extreme tail for pitch, rudders on the fin for yaw, ailerons at the wingtips for roll.
• Authority falls at low speed and high altitude (thin air) — keep speed up on approach.

Reducing drag

• Streamline noses and edges with slopes — slender shapes have dramatically less drag.
• Keep the vehicle compact; spread-out structures present more frontal area.
• Interior blocks are free — only the outer shell is scanned, so internal layout never adds drag.

Watercraft

• Use composite for the hull (best buoyancy-to-weight); use lead low in the keel for stability.
• Wide, flat hulls are the most stable — water damping does the rest.
• Steel/aluminium barely float; use them above the waterline.

Surviving combat

• Symmetry and redundancy: asymmetric wing damage rolls and yaws you, so duplicate critical lifting and control surfaces across both sides.
• Expect a damaged wing to lose lift and drag more — keep speed and altitude in reserve.

Performance

The shape field is cached and only rebuilt when the build changes or takes damage, and its cost is bounded regardless of size or block count. You never pay a per-frame penalty for detail or interior fill — so build as large and as detailed as you like.